1. Field of the Invention
The present invention relates to a contactless power transmission system provided with a power transmitting device including power transmission coils for transmitting power and a power receiving device including a power receiving coil to be magnetically coupled to the power transmission coils.
2. Description of the Related Art
In recent years, there has been known a contactless power transmission system which enables the enlargement of the area of a placing portion and the charging of the power receiving device regardless of at which position of the placing portion the power receiving device is placed by arranging a plurality of coils below the placing portion, on which a power receiving device is to be placed.
For example, patent literature 1 (JP-A 2006-81249) discloses a charging system in which a plurality of power transmission coils and a plurality of communication means are arranged in a desktop mat, the placed position of a notebook PC is detected from the arranged position of the communication means that could communicate with the notebook PC placed on the desktop mat, and power is applied to the power transmission coil located at the placed position.
Further, patent literature 2 (JP-A 2004-229406) discloses a charging system in which a plurality of coils are arranged below a coupling surface of a secondary device, a magnetic field with a magnetic path moving or rotating in the coupling surface is formed by causing currents of different phases to flow into the respective coils, so that power can be transmitted to the secondary device regardless of at which position on the coupling surface the secondary device is placed.
However, since the communication means are used to detect the placed position of the notebook PC in patent literature 1, there is a problem of complicating the system and increasing the cost. Although the magnetic field is so formed that the magnetic path moves or rotates in the coupling surface in patent literature 2, the coils at positions where the secondary device is not placed are also driven since all the coils arranged below the coupling surface are driven. As a result, there is a problem of being unable to promote power saving.